Boron separation and recovery

ABSTRACT

A process is provided for separating, concentrating and recovery of boron compound from aqueous solution containing boron, strongly dissociated anions and some cations. The process specifically integrates electrodialysis with ion exchange to selectively separate boron from aqueous solution that contains a wide concentration range of boron, strongly ionised anions such as chloride, nitrate and sulfate, and cations like lithium. The process is adapted for controlling boron concentration in an industrial process, for the recovery or purification of boron and some cations like lithium form aqueous solutions, and for wastewater treatment.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process for separating, concentratingand recovery of boron compound from aqueous solution containing boron,strongly dissociated anions and some cations. More specifically, itrelates to an integrated process with electrodialysis and ion exchangeto selectively separate boron from the aqueous solution that contains awide concentration range of boron, strongly ionised anions such aschloride, nitrate and sulfate, and cations like lithium. The process canbe used for controlling boron concentration in an industrial process,the recovery and purification of boron and wastewater treatment.

BACKGROUND ART

Most nature waters contain boron in a very low concentration, forexample the boron concentration of a drinking water is usually muchlower than 5 ppm. However, the boron concentration in an industrialprocessing water may be quite different. In the primary coolant ofpressured water reactor (PWR) of nuclear power plant, the range of boronconcentration may vary from 2000 ppm to a few ppm in order to controlthe reactivity of reactor. In addition, a large volume of slightlyradioactive wastewater containing boron primarily as boric acid may beannually generated from this type of nuclear power plant. The wastewateris required for treatment. Therefore, an efficient process or a methodused for boron separation is essential for controlling the industrialprocess and for the wastewater treatment.

Boron compounds like boric acid are widely used as raw material forindustries particularly in the areas of glass, ceramics and enamels.Boric acid is also used as a starting chemical for production of boratesalts, boron phosphate, fluoroborate, borate esters and metal alloys. Acost-efficient process for separation or recovery of boron is requiredfor these industries.

Boron mostly presents as a weakly dissociated anion in normal aqueoussolution. The distribution of boron species depends on the pH ofsolution and the concentration of boron (CRC, 2001). In a lowconcentration of solution with a pH of around 5, most of the boron exitsas boric acid, H₃BO₃, which is an uncharged species. At an increased pHof up to 10 the anion form of boron, H₂BO₃ ⁻, becomes dominant. In ahigh concentration of solution such as in the primary coolant ofpressured water reactor (PWR), boron may be distributed in six speciessuch as boric acid, tetrahydroxyborate (B(OH)₄ ⁻), septahydroxydiborate(B₂(OH)₇ ⁻), decahydroxytriboroate (B₃(OH)₁₀ ⁻),tetradecahydroxytetraborate (B₄(OH)₁₄ ²⁻), andoctadecahydroxypentaborate (B₅(OH)₁₈ ³⁻) (Sperssard, 1970). A generalequilibria among these species can be expressed as follows:xH₃BO₃+yOH⁻

B_(x)(OH)_(3x) ^(−y)  (1)The polymerisation of boric acid easily takes place in a highconcentration of boron solution (B>1000 ppm).

There are serious challenges for the separation and recovery of boronfrom aqueous solution, because boron mostly presents as non-dissociatedboric acid in neutral or weakly basic solutions. The rejection of boronin a reverse osmosis system is low (between 40-60%) under normaloperating conditions, although an increase in the rejection may beachieved at pH of 9.5 or above (Prates et al., 2000). Thenon-dissociated boron cannot be removed by conventional ion-exchangetechnique since ion-exchange resin can only exchange ionised substances.Electrically driven membrane techniques such as electrolysis orelectrodialysis are not suitable for the separation of boron becauseuncharged species cannot be easily migrated in an electrical field(Melnik et al., 1999).

There is an approach to remove boron using boron-selective resins(chelating resins) with diols as the complexing agents of boron (Nadav,1999; Simonnot et al., 2000; Wilcox et al., 2000). However, it isusually expensive and requires a complicated regeneration procedure.Moreover, the recovery of boron requires a selective separation of boronfrom other anions such as chloride, nitrate and sulfates in aqueoussolution.

A technique so-called electrodeionisation (EDI), which combinedelectrodialysis and ion-exchange, was used to remove ionisable speciesfrom aqueous solution by Kollsman et al., (U.S. Pat. Nos. 2,689,826 and2,815,320). Improved EDI systems were disclosed and commercialised byGiuffrida et al., (U.S. Pat. Nos. 4,925,541 and 4,931,160), Ganizi etal., (U.S. Pat. Nos. 5,308,466 and 5,316,637), and Springthorpe et al.,(U.S. Pat. No. 5,868,915) for the purification of waters. The most ofelectrodeionisation systems and apparatus were used for waterpurification and removing relatively low concentration of ionisedcontaminants from water. Although it has been reported that EDI canremove some weakly dissociated anions like carbonates, it is still achallenge for the EDI to remove trace boric acid and silica from aqueoussolution. Moreover, the EDI has not been used for the purposes ofseparation, recovery or purification of weakly ionisable compounds likeboric acid.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to provide anintegrated process for efficient dissociation of weakly ionisable boricacid, by which boric acid can be easily separated through ion-exchangeand electrical migration.

The second objective of the invention is to recover the separated boronand cation such as lithium for further reuse. Therefore the separatedboron and/or lithium should be relatively purified and concentrated.

The third objective of the invention is selectively separation of boronfrom strongly dissociated anions such as chloride, nitrate and sulfateif an aqueous solution contains such contaminant anions.

Another objective of the invention is to improve the efficiency of thesystem by choosing suitable types of ion-exchange resins and theconfiguration of ion-exchange beds filled in an electrochemical cell.

These objectives are achieved by an integrated process comprising:

-   -   separating strongly dissociated anions in the form of electrical        migration performed in one diluting compartment of an        electrochemical cell, which is filled with cation-exchange        materials;    -   separating dissociated cations such as ⁷Li⁺ in the form of        ion-exchange/electrical migration in the same compartment above;    -   separating boron in the form of electrochemical/chemical        dissociation, ion-exchange/adsorption, and electrical migration        performed in another diluting compartment filled by        anion-exchange material only, or a mixture of anion- and        cation-exchange materials, or layers separated between the        anion- and cation-materials;    -   recovering the separated cations into the catholyte compartment        of the electrochemical cell;    -   recovering the separated boron into the anolyte compartment of        the electrochemical cell;    -   recirculating the anolyte in the anolyte compartment;    -   recirculating the catholyte in the catholyte compartment; and    -   recirculating the diluted solution in the diluting compartment        if necessary.

In a preferred embodiment the integrated process comprises:

-   -   an electrodialysis-ion exchange system generally using a        five-compartment electrochemical cell filled with ion-exchange        resins in the diluting compartments as shown in FIG. 1;    -   the separation of boric acid from strongly dissociated anions by        arranging the resin configuration and controlling the DC current        for the electrochemical dissociation of boric acid;    -   the electrochemical dissociation of boric acid by applying a        certain DC current to the electrochemical cell;    -   the chemical dissociation of boric acid by the regenerated        anion-exchange resin filled in the electrochemical cell to        create a relatively high local pH on the surface of resin beads;    -   the adsorption of the dissociated boron on the anion resin, and        the adsorption of dissociated cations on the cation resin;    -   the migration of the adsorbed anions through an anion-exchange        membrane and concentrated in the anode compartment, and the        migration of adsorbed cations through a cation-exchange membrane        and concentrated in the cathode compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical configuration of the system to perform theprocess of the present invention.

FIG. 2 shows a simplified system used for the boron separation from arelatively pure solution containing very low concentration of stronglydissociated anions, in which the separation of boron from the stronglydissociated anions is not considered.

FIG. 3 shows the scheme of pilot testing that was used to demonstratethe process.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The process is performed by an electrodialysis-ion exchange systemtypically consisted of a five-compartment electrochemical cell as shownin FIG. 1. The compartment 1 is a cathode compartment used for therecirculation of catholyte and collecting separated cations. Thecompartment 2 is one of the diluting compartments, in whichcation-exchange material is filled and ionisable anions can directly bemigrated by DC potential through the anion membrane AM into the anolytecompartment (compartment 3). At the same time the cations can also beremoved by ion-exchange/migration through the cation membrane CM intothe catholyte compartment (compartment 1). The compartment 3 asmentioned above is one of the anode compartments used for therecirculation of anolyte and collecting the ionisable anions. Thecompartment 4 is another anode compartment used for the recirculation ofanolyte and collecting the boron removed from the compartment 5. Thecompartment 5 is another diluting compartment, in which anion-exchangematerial is filled, and boric acid is ionised byelectrochemical/chemical dissociation, adsorbed by the anion-exchangematerial, then migrated by DC potential through the anion membrane intothe anolyte compartment 4. The dissociated cations can also be migratedfrom the compartment 5 through the cation membrane into the catholytecompartment.

The process of boron separation and recovery generally involves severalmechanisms. First, boric acid should be ionised byelectrochemical/chemical dissociation. The electrochemical dissociationof boric acid can be considered as a mechanism to be similar to saltsplitting in electrolysis:

It should be mentioned that the boric acid splitting is not easilyperformed in a conventional electrodialysis system, because the electricresistance of non-dissociated boric acid is quite high so that the DCcurrent is limited in a very low level by which boric acid cannot besplit. However, as ion-exchange resin is filled in the dilutingcompartments the resistance of the electrochemical cell is significantlyreduced and high level DC current can be applied for boric acidsplitting.

Secondly, the chemical dissociation of boric acid may also take place onthe resin. Suppose the anion resins have been regenerated in OH form,the dissociation of boric acid should be carried out on the surface ofthe anion-exchange resin beads:R—OH+H₃BO₃

R—+B(OH)₄ ⁻  (3)

Then, the dissociated borate should immediately be adsorbed by theanion-exchange resins.R—+B(OH)₄ ⁻

R—B(OH)₄  (4)

This mechanism has been confirmed by the initial adsorption of boricacid by the well-regenerated anion-exchange resin. It has been foundthat amount of boric acid can be adsorbed by the anion resin regeneratedin OH form even as the pH of the boric acid solution is between 5 to 6.

The chemical dissociation/adsorption may be combined with theelectrochemical dissociation of boric acid, because the quantity of theadsorbed boric acid cannot be explained only by the electrochemicaldissociation of boric acid compared to the corresponding applied DCcurrent.

The another mechanism is the ionic migration induced by electricaldriving force. When direct current is applied between the anode and thecathode, the borate ions adsorbed on the anion resins are migratedthrough the anion membrane into the anolyte compartment.

Finally, water splitting may occur on the surface of ion-exchange resinbeads as an electrical current is applied.

The water splitting provides hydroxyl ions and protons for theregeneration of anion-exchange resin and the regeneration ofcation-exchange resin respectively. This makes the boron separationprocess to be continued.R—B(OH)₄+OH⁻

R—OH+B(OH)₄ ⁻  (7)

The cation separation process can be described as follows. Suppose thecation-exchange resin has been regenerated in H form and boric acid ismixed with LiOH in the untreated solution. The lithium ions for example⁷Li⁺ should directly be adsorbed by the cation resins filled in thediluting compartment during the separation.R—H+Li⁺

R—Li+H⁺  (8)

The lithium ions adsorbed on the cation resins are then migrated throughthe cation membrane into the catholyte compartment.

The cation resins can be regenerated using the protons generated fromthe water splitting (reaction 6). Therefore the cation separation iscontinued.R—Li+H⁺

R—H+Li⁺  (10)

As the solution contains other anion contaminants such as chloride,nitrate or sulfate, the separation of boric acid from the stronglydissociated anions can be achieved in a diluting compartment filled withcation resin. Most of the boron spices are in a non-dissociated formlike boric acid, as the pH of the solution is near neutral or weaklyacid, and if the DC current applied for the electrochemical cell iscontrolled in a relatively low level. Under the conditions above, thestrongly dissociated anions such as chloride, nitrate and sulfate aredirectly migrated from the diluting compartment by the DC potential.However the non-dissociated boric acid is still kept in solution. At thesame time the dissociated cations can also be separated from the anionsand the non-dissociated boric acid.

The separation of boric acid from strongly dissociated anions requires afront diluting compartment filled with cation-exchange material followedby another diluting compartment filled with anion-exchange material. Theconfiguration of front cation resin bed and back anion resin bed shouldbenefit the boron separation because the front cation resin bed providesa good condition for the regeneration of anion resin in the followinganion resin bed.

The process of boron separation and recovery can generally be performedin two models as indicated in FIG. 1. The solid lines show the flowdiagram of a follow-through model. A recirculating model includes thedash line. In addition, the process can be simplified to athree-compartment system as showed in FIG. 2. The simplified process canbe used for the boron separation from a relatively pure solutioncontaining very low concentration of strongly dissociated anions, inwhich the separation of boron from the strongly dissociated anions isnot considered. The simplified process can also be used for the recoveryand purification of lithium like ⁷Li.

The ion-exchange material filled in the diluting compartment 2 (FIG. 1)should be cation resin or other cation exchange materials. Theion-exchange materials filled in the diluting compartment 5 can be asingle bed of anion resin or other anion exchange materials. Thediluting compartment 5 may also be filled with a mixture of cation andanion resins or similar ion-exchange materials, or filled by amultiply-layer bed with separated anion resin and cation resin. Thediluting compartment 6 (FIG. 2) in a simplified process should be filledwith anion-exchange material and cation-exchange material. The resin bedcan be a mixture of the anion resin and cation resin or separatedbetween cation resin and anion resin. The cation resin should be put infront of anion resin if a separated resin bed is used for theseparation. The performance of the system was much better if the mixedion-exchange resins have the same particle size for both cation andanion resins compared to a combination of conventional cation and anionresins.

EXAMPLES

The process of boron separation and recovery is demonstrated in thefollowing examples. A pilot testing of electrochemical cell (FIG. 3) wasused to perform the process. The major specifications of the testingpilot are shown in Table 1. The properties of the ion-exchange membranesand resins used for the tests are given in Table 2 and Table 3,respectively. The initial pH of the boron containing solution used fortreatment ranged from 5 to 6 depending on the concentrations of boronand other species.

In FIG. 3 a catholyte tank is denoted by 1, an anolyte tank is denotedby 2, a diluting tank is denoted by 3, an anolyte compartment is denotedby A, a catholyte compartment is denoted by C, a diluting compartment isdenoted by D, an anion membrane is denoted by AM, and a cation membraneis denoted by CM.

TABLE 1 The major specifications of pilot testing Electrodes Anode: Tibased coated anode (DSA) Cathode: Graphite Membranes Anion-exchangemembrane Cation-exchange membrane Compartment Diluted compartment: 100 ×100 × 7.5 mm volumes Anolyte compartment: 100 × 100 × 2.5 mm Catholytecompartment: 100 × 100 × 5.2 mm Volumes of Diluted tank: 2.000 Lsolutions Anolyte tank: 2.000 L Catholyte tank: 2.000 L Flow modelRecirculation Flow rates Diluted compartment: 0 to 100 L/h Anolytecompartment: 0 to 200 L/h Catholyte compartment: 0 to 250 L/h

TABLE 2 The major properties of the ion-exchange membranes used fortests Manufacture Tokuyama Soda AMX CMX strongly basic strongly acidicTypes anion membrane cation membrane Electric resistance Ω-cm² 2.5-3.52.5-3.5 Brust strength kg/cm² 4.5-5.5 5-6 IX capacity meq/g 1.4-1.71.5-1.8 Thickness μm 160-180 170-190

TABLE 3 The major characteristics of the ion-exchange resins used fortests Manufacture Dow Chemical A1-400 C-400 Gel Gel Types Strong base IStrong acid IX capacity eq/L 1.20 2.20 Water content % 50-60 38-45Particle size μm Uniform Uniform Mean 400 ± 50  400 ± 50  Uniformity 1.11.1 Operating Max. T ° C. 60 130 pH  0-14  0-14

Example 1 Separation of Boric Acid from Strongly Dissociated Anions

This example demonstrates the weakly dissociated boric acid wasseparated from strongly dissociated anions such as chloride, nitrate andsulfate. The separation can be carried out in the diluting compartmentfilled with cation-exchange resin in which both strongly dissociatedanions and cations can be separated from the solution, and the most ofweakly dissociated boric acid cannot be separated. The separation andrecovery of boric acid can be performed in the following dilutingcompartment filled with anion resin or cation/anion resins. In order tominimise the electrochemical dissociation of boric acid, the density ofDC current should be controlled as low as possible. The results in Table4 indicate that boric acid was well separated from nitrate and sulfate.Lowing the DC current could minimise the electrochemical dissociation ofboric acid. It was also shown that the separation of nitrate and sulfatewas not significantly affected as the DC current was reduced to thatlevel.

TABLE 4 The separation of boric acid from strongly dissociated anions*Boron Nitrate Sulfate Current Initial Final Initial Final Initial FinalA/dm² Separat. % ppm ppm Separat. % ppm ppm Separat. % ppm ppm 0.64 21.62031 1593 96.2 5.23 0.20 96.0 4.99 0.20 0.10 9.8 1897 1711 93.2 4.400.30 95.0 6.04 0.30 Note: *The diluted compartment was filled with onlythe cation resin C-400.

Example 2 Separation of Boron from Lithium Using Mixed Anion and CationResins Filled in the Diluting Compartment

The process of boron separation from lithium is demonstrated using mixedresin bed filled in the diluting compartment. As shown in Table 5, boricacid was well separated and recovered by the process. The separationefficiency for both boron and lithium was above 99%. The initial boronconcentration of around 2000 ppm could be reduced to less than 5 ppm.The initial lithium concentration of around 5 ppm could be reduced toless than 10 ppb. The lithium concentration in the separated boronsolution (anolyte) was less than 20 ppb. This indicated that theselectivity of the separation and the purity of the recovered boron arequite high.

TABLE 5 The efficiency of boron separation from lithium using a mixedresin bed in diluted compartment* Boron Lithium Separation Initial conc.Final conc. Separation Initial conc. Final conc. Test No. % ppm ppm %ppb ppb 1** 99.7 2000 5 99.8 3600 8 2 99.7 2019 7 99.8 4850 11 Notes:*The resin bed was mixed with the anion resin A1-400 and the cationresin C-400 in ratio of 4 to 1 in volume. The initial anolyte was 0.1 Mboric acid and the initial catholyte was 0.1 M lithium hydroxide. **Thecation resin was saturated using lithium before use.

Example 3 Separation of Boron from Lithium Using Anion and Cation ResinsSeparated in the Diluting Compartment

The process of boron separation from lithium is demonstrated using theanion resin was separated from the cation resin in the dilutingcompartment. As shown in Table 6, boric acid was well separated andrecovered using a separated resin bed. Although the separationefficiency for both boron and lithium is similar to the separationprocess using the mixed resin bed, it has been found that the electricresistance of the system was lower than using the mixed resin bed.Therefore a high density of DC current should be achieved more easily ina system with separated resin bed than in a system with mixed resin bed.

TABLE 6 The efficiency of boron separation from lithium using a mixedresin bed in diluted compartment* Boron Lithium Separation Initial conc.Final conc. Separation Initial conc. Final conc. Test No. % ppm ppm %ppb ppb 1 99.9 2000 2 99.9 5030 2 2 99.3 2000 14 — — — Notes: *Thecation resin C-400 was filled in front of the diluted compartmentseparated from the anion resin A1-400, and the ratio of anion resin tocation resin was 2:1 in volume. The initial anolyte was 0.1 M boric acidand the initial catholyte was 0.1 M lithium hydroxide.

Example 4 The Concentrating Limit of Boron in the Process of Separationand Recovery

The concentrating limit of boron in anolyte was tested for the processof separation and recovery. The concentration of boron in the anolytecompartment is affected by the solubility of boron, mass transferthrough the anion membrane and electrical migration. The results (Table7) show that the initial solution containing boric acid of 2000 ppmmixed with lithium hydroxide of 5 ppm in the diluting compartment couldbe concentrated as high as 3,5 times in the anolyte compartment. Thisconcentration of recovered boron in the anolyte corresponds to over 80%of the boric acid solubility at 20° C. (Perry, 1997).

TABLE 7 The limit of boron concentration in the collecting solution(anolyte) Boron Final boron concentration separation In diluted Inanolyte Concentrating Test No. % compart. (ppm) compart. (ppm)(final/initial) 1 99.3 13 2974 1.47 2 93.7 126 7077 3.56

Example 5 The Comparison of Various of Ion-Exchange Resins Used for theSeparation Process

The comparison of various ion-exchange resins used for the boronseparation is shown in Table 8. All the ion-exchange resins are thecommercial products of the Dow Chemical. These resins representdifferent types of resin combinations that should be important for boronseparation. The A1-400 and C-400 are gel ion-exchange resins. Theseresins have relatively larger ion-exchange capacities, and the same meanparticle size for both anion and cation resins. The 550A LC NG and 557CNG are nuclear grade gel ion-exchange resins having a normal particledistribution for anion and cation resins. The MSA and MSC aremacroporous ion-exchange resins having relatively large difference inthe particle size between the anion resin and cation resin. As shown inTable 9, the combination of A1-400 (anion resin) with C-400 (cationresin) provided a better current efficiency and more suitable currentdensity than other resin combinations. Because the A1-400 and C-400 havethe same mean diameter and uniform particle size, this should benefitfor flow distribution, electrical migration and mass transfer.

TABLE 8 The comparison of various ion-exchange resins used for theseparation process Average Average Boron current current separationefficiency density Resins* % % A/dm² A1-400 + C-400 99.7 74.2 0.84 550ALC NG + 575C NG 99.6 60.3 0.40 MSA + MSC 99.7 58.7 0.92 Note: *The anionand cation resins were mixed in a volume ration of 4 to 1.

Example 6 The Comparison of Boron Separation with or withoutIon-Exchange Resin Filled in the Diluting Compartment

The tests were performed using the pilot testing without ion-exchangeresin filled in the diluting compartment. The other conditions were keptthe same as that with ion-exchange resins filled in the compartment. Asexpected the separation of boric acid was very low in this system.However the separation of lithium was performed very well. It was findthat the pH of the bulk solution remained in a weakly acidic level inthe diluting compartment and the conductivity of the solution was quitelow. These resulted in a very weak dissociation of boric acid and highelectrical resistance for the system. This may be a good explain for avery low current density during the separation as indicated in Table 9.The low current density made the electrochemical dissociation of boricacid to be difficult.

TABLE 9 The boron separation by the test pilot without ion-exchangeresin filled in the electrochemical cell Boron Lithium CurrentSeparation Initial conc. Final conc. Separation Initial conc. Finalconc. Average % ppm ppm % ppb ppb A/dm² 15.2 2019 1754 99.9 4850 7 0.07

REFERENCES

-   CRC, 2001. CRC Handbook of Chemistry Physics. 82nd Edition    (2001-2002), p. 8-44-45, CRC Press LLC.-   Ganizi, G. C., Wilkns, F., and Giuffrida, A. J., 1994.    Electrodeionization apparatus, U.S. Pat. No. 5,308,466, 1994-05-03.-   Ganizi, G. C., Wilkns, F., Giuffrida, A. J. and Griffin, C., 1994.    Electrodeionization apparatus, U.S. Pat. No. 5,131,6637, 1994-05-31.-   Giuffrida A. J., Jha, A. D. and Gannizi, G. C. 1990.    Electrodeionization method and apparatus, U.S. Pat. No. 4,925,541,    1990-05-15.-   Giuffrida A. J. 1990. Electrodeionization method and apparatus, U.S.    Pat. No. 493,160, 1990-06-05.-   Kollsman, P. 1954. Electrodalytic apparatus, U.S. Pat. No.    2,689,826, 1954-09-21.-   Kollsman, P. 1957. Method and apparatus for treating ionic fluids by    dialysis, U.S. Pat. No. 2,815,320, 1957-12-03.-   Melnik, L., Vysotskaja, O., and Kornilovich, B. 1999. Boron behavior    during desalination of sea and underground water by electrodialysis.    Desalination, 124, 125-130.-   Nadav, N. 1999. Boron removal from seawater reverse osmosis permeate    utilizing selective ion exchange resin. Desalination 124, 131-135.-   Perry, R. H. 1997. Perry's Chemical Engineers' Handbook, 7^(th)    Edition, McGraw-Hill, cop., New York.-   Prates, D., Chilion-Arias, M. F., and Rodriguez-Pastor, M. 2000.    Analysis of the influence of pH and pressure on the elimination of    boron in reverse osmosis. Desalination, 128, 269-273.-   Simonnot, M.-O., Castel, C., Nicolai, M., Rosin, C., Savolin, M. and    Jauffret, H. 2000. Boron removal from drinking water with a boron    selective resin: Is the treatment really selective?Water Research,    34 (1), 109-116.-   Sperssard, J. E. 1970. Investigation of borate equilibrium in    neutral salt solutions. Journal of Inorganic Nuclear Chemistry, 32,    2601.-   Sprongthorpe, P., Giuffrida, A. J., Wilkins, F., Dimascio, F. And    Ganzi G. C. 1999. Electrodeionzation apparatus and method, U.S. Pat.    No. 5,868,915, 1999-02-09.-   Wilcox, D., Montalvo, M., Meyers, P. and Walsh, S. 2000. Boron    removal from high-purity water by selective ion exchange Ultrapure    Water, July/August, 40-51.

1. A process for the separation and recovery of boron from an aqueoussolution of nuclear power plant wastewater containing non-dissociatedboric acid, using a five-compartment electrochemical cell comprising afirst and second diluting compartment, a first and second anolytecompartment, one catholyte compartment, and one anode and two cathodes,whereby a first cation-exchange membrane separates the catholytecompartment from the first diluting compartment, a first anion-exchangemembrane separates the first diluting compartment from the first anolytecompartment, a second anion-exchange membrane separates the secondanolyte compartment from the second diluting compartment, a secondcation-exchange membrane separates the second diluting compartment fromthe catholyte compartment, and an anode separates the first and secondanolyte compartments, the anode being provided with a hole for the flowof anolyte between said first and second anolyte compartments, themethod comprising: feeding untreated aqueous solution to the firstdiluting compartment for separating strongly dissociated anions byelectrical migration performed in the first diluting compartment,wherein the first diluting compartment is filled with cation-exchangematerial only, and separating dissociated cations byion-exchange/electrical migration in said first diluting compartment;feeding the aqueous solution treated in the first diluting compartmentto the second diluting compartment for separating boron byelectrochemical/chemical dissociation, ion-exchange/adsorption, andelectrical migration performed in said second diluting compartment,wherein said second diluting compartment is filled with anion-exchangematerial or a mixture of anion- and cation-exchange materials, or layersof anion- and cation-exchange materials separated from each other;recovering the separated cations into the catholyte compartment of theelectrochemical cell; recovering the separated boron into at least oneof the anolyte compartments of the electrochemical cell; recirculatingthe anolyte in said at least one anolyte compartment recirculating thecatholyte in said catholyte compartment; and recirculating the dilutedsolution in said first and second diluting compartments if necessary. 2.The process according to claim 1, wherein the first and second dilutingcompartments, are separated from the anode by the first and secondanion-exchange membranes, respectively, and wherein the first and seconddiluting compartments are separated from the cathodes by the first andsecond cation-exchange membranes, respectively.
 3. The process accordingto claim 1, wherein DC potential is applied between the anode and thecathode.
 4. The process according to claim 1, wherein the first anolytecompartment is used for collecting the separated strongly dissociatedanions, and the second anolyte compartment is used for recovering theseparated boron.
 5. The process according to claim 4, wherein thedissociated anions are selected from the group consisting of chloride,nitrate and sulfate-ions.
 6. The process according to claim 1, whereinthe catholyte compartment is used for collecting the separateddissociated cations.
 7. The process according to claim 1, wherein aninitial anolyte is a pure solution of boric acid, and an initialcatholyte is a pure solution of a given dissociated cation that may berecovered, and the initial concentrations of the anolyte and catholyteare appropriately adjusted for performing the separation and recovery ofboron and a given dissociated cation.
 8. The process according to claim1, wherein the ion-exchange materials filled in the dilutingcompartment(s) is (are) ion-exchange resins having uniform particle sizeand the same mean diameter of resin beads for both anion and cationresins.
 9. The process according to claim 1, wherein the separation ofboron from strongly dissociated anions is performed before theseparation of boron in the second diluting compartment.
 10. The processaccording to claim 1, wherein electrochemical dissociation of boric acidin the first diluting compartment is reduced by controlling a density ofDC current during the separation of boron with strongly dissociatedanions, the applied current density being controlled below 0.1 A/dm²,and the electrochemical dissociation of boric acid is reduced below 15%as an initial concentration of boron is about 2000 ppm.
 11. The processaccording to claim 1, wherein a DC current applied to theelectrochemical cell is appropriately adjusted to keep a balance amongan electrochemical dissociation of boric acid, the electrical migrationof anions and water splitting for a regeneration of ion-exchangematerials.
 12. The process according to claim 1, wherein the separationand recovery of boron can be performed for an aqueous solution with arange of initial concentration of boron from about two thousand ppm toabout twenty ppm.
 13. The process according to claim 1, wherein a highefficiency of boron separation is achieved, the separation percentage ofboron being over 95%.
 14. The process according to claim 1, wherein ahigh concentrating limit is achieved for boron recovery, theconcentration of boron in the anolyte being up to 80% of the solubilityof boric acid.
 15. The process according to claim 1, wherein theseparation and recovery of boron and a given cation may be performed atthe same time.
 16. The process according to claim 1, wherein thetreatment of the aqueous solution is performed in a recirculating model,a follow-through model or a partial-recirculating model.
 17. The processaccording to claim 1, wherein the dissociated cations are ⁷Li⁺-ions.